Electrical wires are often bundled in cables, either prefabricated or created at the work site. In some applications, cables are used to organize a group of wires carrying coordinated electrical signals from one point to another. In other applications, cables are created primarily for the convenience of handling. When dealing with cables or bundles, it is useful to identify the signals carried by specific wires or equipment being connected by such wires.
Electrical standards, such as the National Electrical Code, have long recognized color coding systems for this purpose. However, it is often expedient to label cables for their individual wires with symbology rather than relying on solely on color codes.
Such labels generally consist of a strip of tape approximately 1.5 inches in length and 0.25 inches in width with adhesive on one side and symbologies on the other. The symbology is reproduced six times on each piece of tape, each line of symbols being parallel to the shorter dimension of the tape. In use, such labeling tape is wrapped with its long dimension circumferentially around the insulation of the cable or wire being labeled. The result is a labeling of the cable or wire which may be easily read, regardless of how it is twisted.
Labeling systems are often used by electricians in the field. "Brady" tape, manufactured by the W. H. Brady Company of Milwaukee, Wisconsin is a typical example of such a labeling system. A Brady system consists of a series of more than 1,000 cards, each card carrying many copies of a given combination of numeric and alphabetic codes. The cards are constructed from a sturdy plastic, approximately 2 inches by 9 inches in dimensions, may be broken away at appropriate points to allow removal of a single piece of labeling tape. For example, a complete set will contain all numerical combinations from 0 to 999 and be able to carry 25 copies of each combination.
To make such a system useful to the electrician, it is essential that a full collection of these cards be carried in the field, and that it be kept in an appropriate order, so that the electrician can efficiently accomplish the wiring job. A full collection of Brady cards is cumbersome and frequently leads to inefficiencies when cards are misfiled or the entire collection is dropped. It is also inefficient for the electrician to be carrying a full set of labeling cards when at most a small fraction of the labels contained on these cards will be used in a given wiring job.
A convenient method for creating wiring labels on demand on the job site without the inefficiencies of carrying a full collection of labeling cards and refiling the cards into the collection is, therefore, highly desirable.